Electron discharge device



Feb. 1, 1944. .1. 1.. H. JONKER 2,349,594v

ELECTRON DISCHARGE DEVICE Filed'gu 21, 1941 i 1 v IQ INVENTORJkazvlHe/bnlia Patented Feb. 1, 1944 ELECTRON DISCHARGE DEVICE JohanLodewijk Hendrik Jonker, Eindhoven,

Netherlands; vested in the Alien Property Custodian Application August21, 1941, Serial No. 407,738 In the Netherlands May 22, 1939* 4 Claims.

This invention relates to an electron discharge device of the variablemu type in which the mutual conductance may be varied or controlled inresponse to control voltages, such as those used in automatic volumecontrol.

The so-called variable mu tubes usually comprise one or more gridshaving a variable pitch or two or more grids between which the distanceis unequal at various points along the grids so as to ensure a gradualdecrease in mutual conductance with increasing negative bias or gridvoltage with reference to the cathode. The anode-current grid-voltagecharacteristic of a variable mu tube may be imagined to be made up ofthe individual characteristics of small parts or portions of the grid.For instance, in a variable mu tube having a grid with apertures ofvarious sizes the smallest apertures through which consequently acamparatively small electronic stream passes will impart to the tube acharacteristic having a steep slope, and to this small stream is thenadded the much larger electronic stream passing through the largeapertures, which impart to the tube a characteristic having much lessslope. This tube characteristic may be imagined to be the resultant orsum of these characteristics for each individual aperture, and is ofgradually decreasing slope. At minimum grid bias the discharge passesthrough all of the apertures, the mutual conductance characteristic ispredominantly that due to the smaller apertures, and therefore its slopeis steep and the anode current is a maximum. As the grid bias increasesand the grid becomes more negative, the discharge through the smallerapertures stops, the mutual conductance is determined principally by thelarger apertures and therefore its slope is less, and the anode currentdecreases. It has been found difiicult to construct such tubes whichhave a very steep slope of the anode current grid voltage characteristicwithout at the same time having an undesirably large anode current atminimum grid bias where the slope is very steep. If the distance betweentwo grids through which the discharge passes in succession is not equalthroughout the length of the grids, the characteristics for differentpoints along a grid will have different slopes, so that electricdischarge tubes having grids between which the distance varies along thegrids will also have a grid voltage-anode current characteristic whoseslope will gradually decrease.

It has been customary to operate a variable mu tubeat different pointsalong this characteristic bvva y ng the ri b as. L ns i ep he d aw backthat upon adjusting the grid bias to operate the tube where thecharacteristic has very steep slope the anode-current is much higherthan necessary for attaining this slope.

The principal object of the invention is to provide a device having amutual conductance which can be readily controlled or regulated so as tovary between high mutual conductance and low mutual conductance withoutchanges in the bias of the control grid, and preferably with a verycontinuous and uniform variation in mutual conductance.

According to the invention the difierent characteristics imparted to thetube by the different portions of the grid are in effect usedindividually and practically unaffected by other portions of the grid.Preferably the device is so made that there can be obtained a verycontinuous transition from one of these characteristics to another, suchas from high mu to low mu. To this end the electron discharge isconcentrated into one or more electron beams shifted along a signal gridof the variable mu typelby beam control or deflecting members.Preferably two or more grid-shaped electrodes are placed in the path ofthe beam so as to'be passed successively by the beam, one of the gridsbeing sufilciently irregular with reference to the othertube elements,as, for example, by being inclined to the other grid to cause the mutualconductance of the tube to vary along the grids in a direction in whichthe electron beam can be deflected. This construction in which thedistance between the signal gridplane and another grid-plane variesalong the grids is a simple way of obtaining an uneven potential in agrid-plane through which the beam pass By varying the difference ofpotential between deflecting members on opposite sides of the electronbeam path the beam can be" directed and the discharge practicallyconfined to difierent sections of the grid which impart difie'rent gridvoltage-anode current characteristics to the tube. If the spaced gridconductors extend parallel with the direction in which the electron beamcan be deflected, the transition between the different characteristicswill be very gradual and will not change abrupty, as mightoccurat'eachaperture if the grid conductors were spaced non uniformlyand extended transversely of the direction ofdeflection of the electronbeam. Thus, according to the invention, a great variation in the slopeof the grid voltage-anode current characteristic is obtainable withoutthe attainrepresents schematically one embodiment ofth'e invention.

The particular embodiment of the device shown in the accompanyingdrawingcomprises an electron discharge tube having an evacuated'enve;

lope l enclosing electrode elements arranged to constitute a variable muor variable amplification factor tube having an anode or outputelectrode 2 and a source of electrons for directing an electron beam tothe anode, such as an indirectly heated cathode 3 and a beam formingelectrode, such as a cylinder 4' coaxial with the cathode and having aslot or opening in one side. The electrons emitted by the cathode areformed into an electron beam 5 which, in the particular con-' structionshown in the drawing, is a flat-sided or'ribbon-like beam substantiallyrectilinear in cross-section and directed to' the anode 2; In-

terposed between the anode and the'source of electrons is a gridelectrode'fi' which comprises a rectangular frame and a plurality ofspaced parallel conductors 1 extending lengthwise of the frame and maybe used as a control grid.

Preferably a second similar grid electrode 8' is interposed between thecontrol grid 6 and the anode 2, and is connected to act" as a screengrid. The control grid 6 is so related to theother elements of the tube,preferably by being inclined to the anode, so that one end is nearer theanode than the other, as indicatedin the drawing, that the gridelectrodes 6' and 8 constitute a grid structure which is sufiicientlyirregular with ref.- erence to the other elements of the tube to givethe tube a difierent mutual conductance or amplification factor atdifierent positions of the beam 5 along the conductors of the grid 6; Inthe particular construction shown the upper end of inclined grid 6 isnearer the anode, and grid 8 is parallel to the anode. at the position Anear the upper end' of'the grid 6, the mutual conductance oramplification factor is high and the tube acts as a' high mu tube, andwhen the beam is near the-other end. of the grid at position B, theamplification factor is low and the tube acts a low mu tube. By shiftingthe beam 5'along the grid 6 lengthwise of the grid conductors l, a veryregular and continuous change in mutual conductance from high mu tolowmu can be obtained. r

The tube may be regulated to operate at will with anyselectedamplification iactor within-the range of the tubeby controlmeans for deflecting the beam lengthwise of the conductors I of the grid6, such as deflection plates Sand lii-positioned between the electronsource and-thegrid 6 on opposite sides ofthe' path ofthe" beam toprovide a passage for the beam. Theposition of the-beam-on the grid6'will depend upon the diflerence of potential between the deflectionplates-'9 and I0, and by varying the potential of the plate ill, forexample, th -beam can bade- When the beam'is flected and held at anyselected point on the rid 6.

For clearness of illustration, the tube is shown as of the elongatedtype, but obviously the tube can be made of cylindrical construction andthe beam 5 instead of being a. flat ribbon-like beam can be a circulardisc beam such as may be obtained by known constructions as, forexample, U. S. Patent to Hamacher, 2,090,001. In this case the two gridsand the anode are obviously in the form of rings or cylinders tocorrespond to the shape. ofthe circular disc beam.

The variation in potential on the deflection plate It] to determine theposition of the beam on the grid 6 maybe obtained in various ways, butfor purposes of illustration, the device is shown for use inautomatic-volume control with the tube connected to a conventionalautomatic volume control circuit of a construction and operation wellknown in the art. As shown, an input circuit ll is connected to thecontrol grid 6 which can be biasedas desired by a grid bias connectionii. The output circuit l3, connected to the anode 2, includes the usualdiode rectifier l4 connected to the conventional diode resistor l5 fromwhich the audio frequency network is supplied. One end of the dioderesistor I5 is connected through the usual filter network IE to theautomatic volume control connection l1 leading to the preceding tubes ofthe set. This automatic volume control connection I! is connected by alead I8 to the deflection plate l0 'so thatthevoltages developed upon.the connection H will be impressed upon the deflection plate. Thecircuit is supplied from the'usualvoltage' divider l9 which isconnectedto the various elements of the circuit and tube in theconventional way.

In operation, the electron beam 5 shaped as a broad thin band or ribbonis deflected along the grid 6 by the deflection plates 9 and It] so thatthis beam impinges on the grid 6 at different points in accordancewiththe differences in potential be tween the deflection plates. Owingtothe diner: ence in spacing between the grids 6 and 8 at differentpointsalong the grids, a dififerentfanode current-gridvoltagecharacteristic is obtained. at different'poi'nts along the grid 6 sothat in accordance with the potential on the deflection plate Hi, thetube will operate with difierent mutual conductance characteristics.When thesignal strength is high, the voltage impressed on the deflectionplate I 0 will be sufficientlyhigh to pull the beam 5 to the position B,where the mutual conductance of the tube is low. When the signal isweak, the voltage on the deflection plate Hi is lower, the beam assumesthe position-A, as shown in thedrawing, and will be directed throughlthecontrol grid fi at a point where the mutualiconductance or mu ofthe-tube is high. Since: the gridconductors I extend in a directionparallel with thedirection' of deflection of the" electron beam, thetransition between'the difierent cha'racteristics at different points ofthe grid liiwill b'e very regular and continuous, with the mu: factordecreasing regularly and continuously as the con trol' voltage onthedeflection plateiii increases with increasing output.

I- claimi 1. An electron discharge tube comprisingan anode, asource'of"electrons for producing an electronbeam to said anode,agridelectrodecomprising elongated gridconductors side byfside andextending-across thepathflof said beam and lying in surface-inclined tosaid anode}- and beamid'e'z flector means adjacent said path forshifting said beam lengthwise of said grid conductors from the endsnearer the anode toward the ends more remote from the anode in responseto an increase in voltage on said beam deflector means.

2. An electron discharge tube comprising an anode, a cathode, beamforming means for forming the discharge from said cathode to said anodeinto a flattened beam, a pair of flat insulated parallel beam deflectionplates spaced apart and providing a passage for the beam with the platesalongside the broad sides of the passage, and a grid electrode betweensaid deflection plates and said anode comprising spaced parallel gridconductors extending across the path of said beam, 1;

each of said grid conductors being inclined at the same angle to saidanode.

3. An electron discharge tube comprising an anode, a source of electronsfor producing an electron beam to said anode, two grid electrodespositioned side by side between said source and said anode to be passedin succession by said beam, one of said grids comprising spaced para1lel grid conductors inclined to said anode, and a pair of insulated beamdeflection plates between said source and said grids spaced apart'andproviding a passage between them for said beam to deflect said beamalong and lengthwise of said conductors from the end nearer the anodetoward the other end in response to increase in difference of potentialbetween said deflection plates.

4. An electron discharge tube comprising an anode, a source of electronsfor producing an electron beam to said anode, two grid electrodespositioned side by side between said source and said anode to be passedin succession by said beam, one of said grids being inclined to saidanode, a pair of insulated beam deflection plates between said sourceand said grids spaced apart and providing a passage between them forsaid beam to deflect said beam along said inclined grid, each of saidgrids comprising spaced elongated parallel conductors extending acrossthe path of said beam in the same direction as the beam is moved by saiddeflection plates.

JOHAN LODEWIJK HENDRIK JONKER.

